The elucidation of the electron-transport mechanism of cytochrome c, electron capture from cytochrome c1 and donation to cytochrome c oxidase, is the objective of this proposal. The specific modification of protein functional groups with group-specific reagents, both localized on the surface and buried in the heme crevice area, and investigation of physiological function, molecular conformation, the redox potential of heme iron and the kinetics of the electron capture and donation capabilities by and to non-physiological electron donors and acceptors constitute the basic approach. The correlation of results in terms of the role of various protein functional groups in determining the protein conformation and physiological function, including the characteristics for the binding of the neighboring electron-transport chain components, will lead to elucidation of a possible path, the binding sites and the structural details of electron flow.